This invention relates to cataract extraction and lens implants, and more particularly, to an intraocular lens implanted in the capsular bag or ciliary sulcus after extracapsular cataract extraction.
Intraocular lenses are used to restore vision in patients whose cataracts have been extracted. A cataract is an opacity or the loss of transparancy of the crystalline lens of the eye. The opacity may be minimal in size and faint in density so that the transmission of light is not appreciably affected, or it may be large and opaque so that light cannot gain entry into the interior of the eye. A cataract is removed if it endangers the health of the eye or seriously impairs the patient's ability to function. Usually a cataract is not removed for visual purposes until the vision in the better eye has deteriorated to at least 20/50.
In a cataract operation, the lens is removed to extract the cataract from the eye. The lens may be removed from the eye by (1) an intracapsular cataract extraction which consists of complete removal of the lens within its capsule through a superior limbal incision, and (2) an extracapsular cataract extraction in which the lens and center portion of the anterior capsule are removed, leaving the capsular bag, i.e. the posterior capsule and remnants (folds) of the anterior capsule. In an extracapsular operation, a superior limbal incision is also made, the anterior portion of the capsule is ruptured and removed, the nucleus is extracted, and the lens cortex is either irrigated or aspirated from the eye. Some patients develop a secondary opacity of the posterior capsule which requires discission. The extracapsular operation is preferred in older patients to reduce long term postoperative vitreous and retinal complications. Extracapsular operations are also very useful for patients with high myopia and retinal degeneration, or previous retinal detachment in the same eye. The extracapsular method is also preferred for individuals under 30 years of age, including children with congenital cataracts. The extracapsular method is particularly adapted to the eye of the young patient because the nucleus of the lens is soft.
Extracapsular cataract extraction is best done when a cataract is complete or mature (ripe). In such lenses the cortex is degenerative and fluid, and is readily irrigated from the eye after the hard nucleus is removed first, usually by external pressure upon the eyeball. If the cataract is incipient or immature, the lens cortex is viscid and tenacious, and significant amounts of it may remain adhered to the retained posterior lens capsule which can cause severe inflammatory reactions. Diseased lenses with cataracts are removed through a small incision at the edge of the cornea.
When the natural lens has been removed in accordance with extracapsular cataract extraction, unfocused light reaches the retina and causes blurring, and post-operative eyeglasses not only magnify greatly but provide little side vision. Intraocular lenses reduce the magnification markedly and widen the field of vision. Intraocular lenses are particularly helpful for patients who cannot insert and remove contact lenses by themselves, such as victims of rheumatoid arthritis and Parkinson's disease and some children. Intraocular lenses also usually provide better binocular vision and causes less aniseikonia than contact lenses.
Most surgeons prefer to perform a cataract extraction and insert the intraocular lens during the same procedure. The intraocular lens is placed into the anterior chamber, aligned with the optical portion of the eye, and wedged in the pupillary aperture. Two types of artificial lenses commonly used are the iris fixation type, which usually results in a square pupil, and the iridocapsular fixation type, which uses the iris and the posterior lens capsule.
Over the years numerous intraocular lenses have been developed. Many of these prior art intraocular lenses, however, are unstable, ineffective, easily dislodgable, dislocate, or change positions, causing discomfort, blurriness, optical misalignment or secondary glaucoma. Typifying some of the many intraocular lenses that have been suggested are those found in U.S. Pat. Nos. 4,315,336; 4,315,337; 4,316,291; 4,316,292 and 4,316,293.
It is therefore desirable to provide an intraocular lens which overcomes most, if not all, of the preceding problems.